1. Field of the Invention
The present invention relates to a communication system. More particularly, the present invention relates to an apparatus and a method for allocating a channel and power in a multi-cell communication system.
2. Description of the Related Art
In order to efficiently provide high-speed large-capacity services, the next generation communication system needs to maximize frequency efficiency. In order to increase the frequency efficiency, a Wireless Metropolitan Area Network (WMAN) communication system, for example, needs to divide the whole network into multiple cells, and needs to support the reuse of frequency resources in each of the multiple cells. However, when the frequency resources are reused, Inter-Cell Interference (ICI) occurs, which causes significant performance degradation for users who are located on a cell boundary among users in each cell.
The reuse rate of the frequency resources is expressed as a frequency reuse factor. The frequency reuse factor indicates the number of cells, to which a frequency band is distributed. When the frequency reuse factor is set to a value more than “1,” frequency efficiency becomes lower, but ICI becomes smaller. Therefore, a Fractional Frequency Reuse (FFR) scheme, in which a frequency reuse rate is controlled for each subchannel by using a trade-off between frequency efficiency and ICI according to the frequency reuse factors, has been proposed for use in the next generation communication system. The FFR scheme refers to a scheme in which a frequency reuse factor is set to “1” for some subchannels and is set to a value more than “1” for the remaining subchannels.
In the FFR scheme, a frequency reuse pattern is determined and fixed during cell planning. However, a frequency reuse pattern for optimizing frequency efficiency changes depending on user distribution in a network, the number of users in each cell of the network, etc. In the FFR scheme, it is impossible to control the frequency reuse pattern in response to changes in the network as described above. Therefore, when the FFR scheme is used, there is a problem in that system performance is degraded. Also, when the FFR scheme is used, it has limitations in performing power control through the frequency reuse pattern. Therefore, there is another problem in that power cannot be efficiently controlled. Consequently, there has been a demand for a scheme for allocating an optimal frequency channel and optimal power in adaptive response to a network state which changes depending on user distribution in a network, the number of users in each cell of the network, etc.